The present invention relates generally to a tablet device that inherently has a position detecting function for detecting an indicated position thereon defined by a combination of associated coordinates as a position data to be input to a certain device coupled therewith, and particularly, to a tablet device integrated with a display device that inherently has an image display function, or in other words, to an integrated tablet device having both the position detecting function and the image display function.
1. Description of the Related Art
FIG. 1 shows an exploded view, in part, of a typical conventional tablet device.
The typical conventional tablet device includes a sheet-like tablet member 48 assembled with a sheet-like display member 47. The members 47 and 48 are fabricated as separate products and tight-sticked together. Designated at reference character 49 is a pen member for pointing a position on the tablet member 48 to generate a position signal.
The display member 47 may comprise e.g. a liquid crystal display. The tablet member 48 may be e.g. an electro-static capacitive coupling type.
Such a conventional tablet device including a tablet member assembled with a display member separately fabricated has an undesirable weight and an undesirable volume of which undisregardable fractions are attributable to the tablet member, respectively, in addition to that it needs a costly assembly process.
Still more, in use of such the conventional tablet device, the tablet member which intervenes between the display member and a point of a pen member tends to cause a parallax so that the pen point may be located at a position deviated from a position to be indicated on the display member.
To solve such conventional problems, the Japanese Patent Application Laid-Open Publication No. 2-255911 has proposed a tablet device in an integrated form having both a position detecting function and an image display function.
This conventional integrated tablet device comprises an image display system including a display member, and a position detecting system for detecting a pointed position on the display member.
The image display system comprises the display member which is composed of a thin-film EL (electroluminescence) panel consisting of a matrix of EL pixels, a row electrode driver for sequentially driving to scan respective rows of the pixel matrix, via their bus lines, a column electrode driver for selectively driving respective columns of the pixel matrix, via their bus lines, so that selected ones of scanned pixels are operated to display an image, and a timing generator for generating a timing signal to control the drivers, as well known.
The position detecting system comprises: in a wide sense, a coordinate defining system for defining a set of coordinates on the display member, a pen as a position pointing member for pointing a position on the display member, and coordinate detecting circuitry, connected to the coordinate defining system, the pen and the timing generator, for detecting a combination of coordinates of the pointed position: and in a narrow sense (as used herein), the coordinate defining system and the coordinate detecting circuitry.
The coordinate defining system comprises the row and column electrode drivers and the row and column bus lines of the image display system, as the bus lines are sequentially scanned by applying scan pulses from the drivers in a coordinate detection mode such that, when a bus line corresponding to a position pointed by the pen is scanned, the pen senses a significant potential due to an electrostatic capacitive coupling in a vicinity of the pointed position, which potential is input to the coordinate detecting circuitry, where it is detected as a coordinate represented by the scanned bus line.
The scan pulses may be superimposed on pixel drive signals, or may be applied during a position detecting period separated from an image display period in a time-dividing manner.
In the conventional integrated tablet device, the image display system of a thin-film EL type, in which the pixel driving bus lines are commonly employed as an essential part of the coordinate defining system, may theoretically include an active-matrix type liquid crystal display (hereafter "TFT-LCD") having a matrix of pixels using a thin-film field effect transistor (hereafter "TFT").
FIG. 2 is an exploded perspective view, in part, of a typical TFT-LCD.
The typical TFT-LCD comprises an unshown timing signal generator, an unshown gate drive circuit, an unshown source drive circuit, and a display member provided with an unshown light source.
As partially shown in FIG. 2, the display member comprises a TFT substrate 50, an counter electrode 54 facing the TFT substrate 50, and a quantity of unshown liquid crystal filled in a gap between the TFT substrate 50 and the counter electrode 54.
The TFT substrate 50 is formed with a matrix of switching TFTs, a multiplicity of parallel gate bus lines 51 for connecting the gate drive circuit to gate electrodes of TFTs in rows (or columns) of the TFT matrix, a multiplicity of parallel source bus lines 52 for connecting the source drive circuits to source electrodes of TFTs in columns (or rows) of the TFT matrix, and a matrix of pixel electrodes 53 one-to-one connected to drains of the TFTs.
Each pixel is composed of one of the pixel electrodes 53 connected, a corresponding area of the counter electrode 54, and a corresponding volume of liquid crystal resting therebetween so that a pixel capacity 55 is established thereacross.
The TFT-LCD of FIG. 2 may be employed as a direct-view personal display of either of two back-lighted types. In a first back-lighted type, the light source is located (in FIG. 2) above the counter electrode 54, which thus intervenes between the light source and the TFT substrate 50 which faces a user. In a second back-lighted type, the light source is located (in FIG. 2) under the TFT substrate 50, which thus intervenes between the light source and the counter electrode 54 which faces a user.
The TFT-LCD of the second back-lighted type is now supposed to be employed as an image display system of an integrated tablet device so that, in a coordinate detection mode, the gate and source bus lines 51 and 52 constitute a coordinate defining system to which the gate and source drive circuits supply coordinate identifying scan pulses.
In the coordinate detection mode, a pen member is to point a position on an external surface of the counter electrode 54, which intervenes between a user and the TFT substrate 50 on which the bus lines 51 and 52 are formed.
In this arrangement, however, the counter electrode 54 constitutes an electrical shield member so that it may be difficult to effectively detect, by way of an electrostatic capacitive coupling, a coordinate identifying scan pulse supplied to one of the bus lines 51 and 52.
Still more, the source drive circuit, which inherently is adapted to supply image signals, is needed to serve for supplying the coordinate identifying scan pulses in a superimposing manner or time-dividing manner, thus resulting in significant increases such as in complexity, weight and volume of associated circuitry.
The present invention has been achieved with such points in mind.